Exploring phosphatase and tensin homolog (PTEN) loss via immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) as a potential predictive marker for response to everolimus in patients (pts) with neuroendocrine tumors (NET).

Abstract

333 Background: Identification of pts with exquisite sensitivity and/or durable responses to targeted therapies may lead to improved patient selection and allow for more rational treatment designs. Exceptional responders to everolimus in NET including pancreatic (PNET) were observed in our cohort of pts. PTEN is a key negative regulator of the phosphatidylinositol 3-kinase(PI3K)/Akt and mammalian target of rapamycin (mTOR) pathway. Loss of PTEN tumor suppressor gene function, usually due to deletion, leads to PI3K/Akt/mTOR pathway activation. Inthis study, we explored the role of PTEN as a potential predictive marker of everolimus in pts with NET including PNET. Methods: Between 2010 and 2014, pts with well-differentiated unresectable and metastatic gastrointestinal NET treated at our institution with everolimus were identified. 17 patients had pathology specimens available for testing. PTEN loss detection by FISH was carried out using a commercially available probe for cytoband 10q23, and by IHC using a commercially available antibody. Patients’ response to everolimus was evaluated through August 2014. The primary outcome was PFS and PTEN status was correlated with PFS for any potential association. Results: The median age was 59 years (range 45-78); 7 were male; 8 had PNET (2 gastrinomas, 1 insulinoma and 5 non-functional); 7 had small bowel NET and 2 unknown primary. All pts received everolimus starting at 10mg daily and octreotide LAR. Of the pts with PNETs, 3 had PTEN loss by FISH. Of those, one did not tolerate everolimus. The PFS for the other two pts was 8 and 24 months respectively. Among the 4 pts with intact PTEN; PFS was 14, 26, 3 and 12 months. 1 patient had insufficient tumor for testing. PTEN FISH is ongoing in the 9 non-pancreatic NET pts. PTEN expression by IHC is also ongoing and will be reported at the meeting. Conclusions: Testing for PTEN loss by FISH is feasible. Due to the small sample size, the role of PTEN loss could not be defined as a predictive marker in PNET. Testing on additional cases is ongoing and will be presented at the meeting.